420 THE LAWS OF ORGANIC 



elude, that epistaxis and hemoptysis have not the 

 same proximate cause as apoplexy. 



DXIL It is stated, that the sudden removal of 

 atmospheric pressure distends the external blood- 

 vessels in the same manner as heat. There is a cer- 

 tain seeming coincidence in the phenomena that 

 tkese present : but if we narrowly investigate the cir- 

 cumstances in which they resemble each other, we 

 shall perceive a great difference in the origin and 

 influence of their peculiar properties. Heat does 

 not simply distend the blood -vessels, but more par- 

 ticularly rouses the circulation, and gives rise to 

 those general consequences described in DV., but 

 particularly in Chapter VIII. The removal of 

 atmospheric pressure does not immediately sti- 

 mulate the vessels upon the surface of the body, 

 but allows the blood to flow here with greater 

 facility, and gives to the vessels a degree of ful- 

 ness and distention, not unlike the appearance ex^ 

 bited by an increase of temperature ; but when 

 such is the consequence of heat, the internal or-r 

 gans are not only relieved by a diminution of 

 blood, but are likewise excited by the stimulus 

 conveyed to the respiratory and circulatory func- 

 tions ; but, in case of diminished pressure, no sti- 

 mulus whatever is communicated to these, except 

 such an improvement of energy as may follow the 

 change in the distribution of the blood. 



J3XIII. Philosophers not being fully acquaint- 

 e4 with the alterations whicfy the circulation 



